The treatment and recovery/recycling of automobile, industrial, commercial, construction, demolition, agricultural and municipal solid wastes and waste streams presents a substantial problem in most of the world's countries, developed, industrialized and underdeveloped alike. The vast diversity of the particular components of solid wastes and waste streams; the variability of quantity of each particular component with time and/or geographic location; the technical challenge to processes, apparatus and techniques to successfully divide these components into recoverable, substantially separate, non-intermixed (product) fractions; the variability in equipment and utilities costs, together with variability in value of any recovered products due to market conditions, transportation costs, and other factors, all combine to make solid waste treatment extraordinarily complex in conception and execution. The viable proposed solutions are many and diverse, and all are subject to shortcomings of different and varying degree. So complex are the problems presented, that attempts to treat and recover/recycle may not even be contemplated. Other solutions to handling solid wastes and waste streams may seem the only possible choice, particularly the "burn and/or bury" approach of incineration followed by landfill, or direct landfill.
Landfill has traditionally been a technique used to dispose of many types of solid wastes and waste streams. But the world is running out of places to dig convenient, cost-effective and environmentally-acceptable holes, especially in Europe, where several countries are planning to or will ban landfills within the next five (5) years. Incineration has been another traditional technique that has been severely curtailed due to high capital costs and environmental (air pollution, water pollution) concerns. Both procedures often suffer from poor economics as well: it is difficult to extract maximum value from these waste streams, when burying and burning makes many potentially recoverable components inaccessible, or consumes them only for heat values.
Separation and recovery/recycling of solid waste and waste-stream components has a long history, with a myriad of techniques, processes and devices having been assayed and applied, with widely divergent "success" and, often, partial or total failure to present a reasonable solution to the problem. Costs and complexity of separation, particularly the inability to provide clean/perfect separation of recoverable fractions, are the usual drawbacks, delivering a body blow to many recycling processes where the process costs more than the resulting recovered/recoverable materials are capable of generating in the market. The key to recycling of solid wastes and waste streams lies in discovering and recovering that within the waste that assures the economics and efficiency of its own recovery and recycling.
The quantity of waste to be treated has a direct effect on the ability to use known processes for separation and recovery of components, and/or the cost-effectiveness of those processes. Only processes that offer the ability to operate continuously to process very high volumes/through-puts, often appear viable when compared to the "bury or burn" alternatives, if available.
Known waste recovery and recycling techniques use a vast array of unit operations and devices for solid waste processing and separation:
size reduction, by means of grinders, shredders, pulverisers and fragmentisers; PA1 classification, by means of cyclones (single or multiple), trommelscreens and accordion screens; PA1 concentration, by means of eddy currents and air separators; PA1 separation, by means of magnets, cyclones, vibratory screen bins and heavy liquid medium separation vessels; PA1 dewatering, by means of sieve beds, vibratory screens and trommelscreens; PA1 rinsing, by means of vibratory screens, rinsers and scrubber-rinsers; PA1 decantation, by means of clarifiers and deep cones; PA1 pressing, by means of screw presses, hydraulic presses and filter belt presses; PA1 thermal decomposition of organic residues by means of thermolysis ovens; PA1 vitrification of inorganic residues, by means of liquid metal reactors and vitrification ovens; and PA1 the generation of compost or equivalent bio materials. PA1 ferrous metals, recycled as bars, ingots, profiles and plates; PA1 light organics, such as paper, cardboard and wood, recycled as cellulose building blocks; PA1 light organics, such as textiles and foam rubber, recycled as gas and carbon; PA1 heavy organics, such as rubber, wood and plastic, recycled as gas and carbon; PA1 heavy organics, such as rubber, wood and plastic, directly fed to cement kilns; PA1 light and heavy organics recycled as carpeting and insulation; PA1 glass recycled as glass; PA1 glass and other inorganic residues vitrified and subsequently incorporated into cement; PA1 glass and other fine inorganic residues vitrified and recycled as artificial granite; PA1 magnesium recycled as powder and ingots; PA1 aluminum recycled as ingots and castings; PA1 heavy metals isolated as a group of heavy metals for further separation and processing; PA1 garden waste recycled as activated carbon and solid fuel; PA1 forestry waste recycled as activated carbon and solid fuel; PA1 food and agricultural waste recycled by means of compost and bio material. PA1 Heavy Medium Separation (HMS), alternatively known as Dense-Medium Separation, sink-float separation, or sink and float, is essentially the simplest and one of the most widely applied gravity concentration processes both in minerals treatment and in coal preparation. It is a process applied to the separation of minerals in a liquid or a fairly stable suspension of a predetermined density, chosen such that the density is higher than the lighter constituents and lower than the heavier constituents. In this respect it differs from all other gravity concentration processes, where the medium (generally water) is of a density lower than all the constituents in the ore. PA1 There are two major areas of application for heavy medium separation. It can be used to produce a commercially saleable end product, such as in coal preparation--where it is one of the two primary means of cleaning coal from the shale--and in some industrial minerals applications. Alternatively it can be used to produce an economically acceptable waste product which does not warrant the cost of further treatment: in this case it is a preconcentration device and as such is of major importance in the preconcentration of diamonds, sulphides and metal oxides. PA1 The size range of applicability of the process is large. PA1 In a static separator HMS vessel, the essential separating force is gravitational and the essential counter force is the resistance to viscous shear. If a range of particles of different specific gravity and size are placed in a fully static vessel filled with a true liquid of a density between the highest and lowest specific gravities of the particles, then those particles with a specific gravity exactly equal to the liquid density will hover. All other particles will, given sufficient time, either sink or float (unless they are so small that Brownian movement becomes significant). PA1 Commercially, suspensions are generally employed, which, although comparatively stable, do have a low rate of settlement. PA1 In dynamic separation, the forces tending to separate heavies and lights are much greater. With a typical cyclone the centrifugal force on a particle at the inlet is up to 20 times the gravitational force in a static bath (Sokaski and others 1968); it is an order of magnitude higher again at the apex. This increased force acts not only on the ore to be separated but on the medium as well and the density of the medium flowing through the apex (heavies) is significantly higher than at the inlet: conversely the density of the medium at the vortex (lights) is significantly lower than at the inlet. PA1 Heavy medium separation, suitably controlled, has the ability of sharp separations at any density within the limits of the medium chosen, and, at very high efficiency, even in the presence of a large proportion of near density materials. The density of separation can be closely controlled, under normal conditions, almost indefinitely within 0.005 e.g. units, but conversely can be rapidly changed if required to meet new operating requirements. PA1 In operation, the feed must be screened to remove fine ore and slimes prior to it being fed, with reconstituted medium into the separator vessel. Floats and sinks are withdrawn separately and drained, on static or vibratory screens, of the majority of the medium which returns either direct to the system or is cleaned prior to return. Next, the floats and sinks are washed, on vibratory screens to remove essentially all the remaining adhering heavy medium. PA1 The undersize products from the washing screens, consisting of medium, wash water, and fines, are too dilute and contaminated to be returned directly as medium to the separator vessel. They are treated individually, or together, by magnetic separation, to separate the magnetic ferrosilicon, or magnetite, from the non-magnetic fines. Reclaimed, cleaned medium is thickened to the required density by a suitable classifier, which continuously returns it to the HMS circuit The densified medium discharge passes through a demagnetizing coil to assure a non-flocculated, uniform suspension in the separator vessel (Wills 1981, Gochin and Smith 1983). PA1 The circuit must be regarded as a whole for both design and operational purposes. Equipment for each stage must be matched with the rest of the circuit, both in terms of capacity and performance. PA1 Vessels fall into two broad classifications: static and dynamic. There are several differences between them, although the basic principles remain the same: light particles float and heavies sink. In stationary vessels, the separation, generally of particles coarser than 3 mm, is carried out at normal gravity; whilst in dynamic systems finer particles (down to 0.5 mm) are separated at an elevated gravity. Static vessels contain significantly more medium than dynamic vessels. Consequently, the residence time in static vessels is considerably longer than in dynamic vessels. PA1 Static vessels can be subdivided into cone, drum, trough and combination types. The feed is generally introduced at, or near the top of the separator vessel. Light particles float on the surface and are removed over a weir, with a portion of the medium, with or without the assistance of paddles. Removal of the sinks varies from type to type. In cone separators sinks are removed by an internal or external airlift, by pump, or a chain elevator; the sinks from drum separators are normally removed from the medium by lifters mounted inside the drum; in trough separators the sink is removed by chain conveyor or skimmer bar; whilst in combination baths the heavies, having settled through a comparatively shallow, static bath are elevated by a device outside the main bath. PA1 Cone separators are ideally suited to the treatment of coarser coals, in the size range of 100 to 3 mm, especially in the U.S.A., as they handle large quantities of lights, but are less amenable to handling large quantities of sinks. Drum and trough separators, on the other hand, are capable of handling large quantities of sinks which makes them popular in the mineral field where the proportion of heavies can reach 80% (Wills 1981) and in European Coal Preparation plants where often over 50% of the feed will be heavies. The size range of material suitable for these shallow bath separators is 1 m to 6 mm. PA1 Drum separators are popular heavy medium separation units both in the mineral and coal preparation fields, for separation of feed materials in the range of 5-250 mm. PA1 Drum separators, as their name implies, consist essentially of a rotating cylindrical drum, fitted with lifters on the inside of the drum to elevate the heavies out of the medium bath. PA1 The Wemco Drum (Fig. 9.6. and 9.7.) is typical of the drum separator type, and it can be used for two or three product separations. The single compartment drum (Fig. 9.6a) is used for single gravity, two product separations, whilst in the two compartment drum, a radial partition divides the drum into two, each compartment operating independently, either: PA1 Longitudinal partitions within the drum segregate the lights, on the surface of the medium, from the revolving heavies lifters. The comparatively shallow pool depth in the drum compared with the cone separator minimizes settling out of the medium particles giving a uniform gravity throughout the drum. PA1 The Hardinge Counter Current Separator is a rotating drum with a length approximately twice its diameter. To the inside of the drum are fixed spiral flights increasing in height from the feed end to the discharge end. The whole unit is set at a slope of approximately 5 degrees, with the last row of spiral flights exposed above the pool level. PA1 The spiral flights move heavies in the opposite direction to the lights, and they are elevated by lifters to the heavies discharge chute. PA1 Whatever type of vessel used, there are certain basic requirements for efficient operation: it should have a high unit capacity related to area; it must allow for efficient feed presentation and product removal; it should require the minimum of circulating medium; hydraulic currents within the vessel should be minimized (difficult in dynamic systems) and it should be capable of accepting particles of widely differing size, shape and specific gravity, but separating them on the basis of specific gravity alone. PA1 It is a general object of the invention to provide a completely self-contained, nonpolluting, hydromechanical apparatus for lead-acid battery constituent separation which performs simultaneously several important steps in such separation, heretofore performed successively, by combining a multiplicity of separate processing stations into a single, all-purpose processing stage. PA1 1) The proper introduction of the feed material into the bath is the first requirement in making a good dense medium separation. In a '946/'949 bidirectional separation vessel, the feed material drops into an injector filled with a fast-moving stream of liquid medium. The medium plus solids enter the separation zone where they are well distributed over a broad three-dimensional front, thus preventing floats from being entrapped with sinks. PA1 2) A stable and uniform density throughout the bath is the second requirement. In a '946/'949 bi-directional separation vessel a stable medium is assured by the bi-directionality of the drum and by operating the vessel to maintain a shallow depth of the bath (40-50 cm). Bi-directionality creates a gentle counter-current flow dynamic which maintains a stable and uniform density throughout the bath. PA1 3) No error on the float side of the barrel is the third requirement. A '946/'949 bi-directional separation vessel may be built to have a very long separation zone, 4 to 5 meters in length, which assures a very long residence time of the feed material in the separation zone. A long separation zone free of turbulence allows for an extremely accurate separation. Also, there are no paddles moving floats along, as in the known Drewboy separator; there is no lifting of sinks in the separation zone, also as in most mono-directional barrels; there are no curs in the separation zone, as in most mono-directional barrels; and there is no sinks evacuation chute in the separation zone, as in most mono-directional barrels. Without all of these devices in the separation zone, the full surface of the bath is available for separation, and, most importantly, all unnecessary turbulence is eliminated. A 2.4 meter diameter '946/'949 bi-directional drum can handle more than 100 TPH of floats, and a 3-meter diameter bidirectional drum can handle more than 200 TPH of floats. PA1 4) No error on the sink side is the fourth requirement. In bi-directional separation vessel, a curtain may be provided to prevent floats from crossing over with sinks, which is situated completely outside the separation zone. Sinks are lifted up preferably by means of a scrolled cone, but only when completely outside of the separation zone. Since the drum can be rotated as much as 20 rpm, in current design, this provides substantial sinks evacuation capacity, with little danger of floats reporting with sinks. A 2.4-meter diameter '946/'949 bi-directional drum with a curtain can evacuate more than 50 TPH of sinks, and a 3-meter diameter barrel can handle more than 100 TPH of sinks. PA1 1) Because of its large surface area relative to its mass, porous material responds poorly to the float/sink dynamic of a Newtonian liquid; PA1 2) Because porous material absorbs the suspension media used in creating the liquid medium, problems are presented in that these suspension media cannot be recycled economically; and PA1 3) Because porous material absorbs water, it would exit a dense medium bath at a relatively high moisture content, and the economics of its later disposal would be placed in jeopardy. PA1 (a) a first separation stage, further comprising introducing said heterogeneous mixture into a first separation vessel, containing a first liquid medium having a first specific gravity of about 1.0, such that said heterogeneous mixture contacts said first liquid medium, a first part of said mixture rising in the liquid medium as float particles, the remaining part settling in the liquid medium as sink particles, whereby porous materials present in said heterogeneous mixture having a specific gravity of less than about 1.0 are substantially separated as said float particles; (b) removing said float particles from said first vessel, to recover a porous product material; (c) removing said sink particles from said first vessel; (d) a second separation stage, further comprising introducing said sink particles from said first separation stage into a second separation vessel, containing a second liquid medium having a second specific gravity, different from the specific gravity of said first liquid medium, said liquid medium including a waste-derived particulate suspension media component present in a quantity sufficient to attain said second specific gravity, such that said sink particles contact said second liquid medium, a first part of said particles rising in the liquid to form float particles, the remaining part settling in the liquid medium as sink particles, whereby organic materials present in said sink particles from said first separation stage are substantially separated as float particles; (e) removing said organic float particles from said second vessel as a substantially organic particulate mixture; and PA1 (a) a first separation vessel for receiving said heterogeneous mixture, containing a first liquid medium having a first specific gravity of about 1.0, which medium contacts said heterogeneous mixture, for causing a first part of said mixture to rise in the liquid medium as float particles, and the remaining part to settle in the liquid medium as sink particles, said vessel including means to remove said separated float particles without intermixture with said sink particles and means to remove said separated sink particles without intermixture with said float particles; and (b) a second separation vessel for receiving said sink particles from said first separation vessel containing a second liquid medium having a second specific gravity different from the specific gravity of said first liquid medium, said second liquid medium including a waste-derived particulate suspension media component present in a quantity sufficient to attain said second specific gravity, which second medium contacts said sink material, for causing a first part of said material to rise in the liquid medium as float particles, and the remaining part to settle in the liquid medium as sink particles, said vessel including means to remove said separated float particles without intermixture with said sink particles, as a substantially organic particulate mixture, and means to remove said separated sink particles without intermixture with said float particles, as a substantially inorganic particulate mixture.
Depending upon specific application to automobile, industrial, commercial, construction, demolition, agricultural and/or municipal solid wastes and waste streams, a separation and recovery/recycling process may generate a variety of products (comprising fractions or components of the heterogeneous waste stream feed) and by-products of differing potential value:
Ideally, a separation and recovery/recycling system and process would present the capability and flexibility to handle substantial daily through-puts, in the tens to hundreds of tons per hour range, which may vary from day to day as to both total quantity and identity and nature of components present, coming from a variety of solid wastes and waste stream sources, including automobile, industrial, commercial, construction, demolition, agricultural and municipal solid wastes. The separation and recovery of separation products would generally provide materials falling within a group of broad categories if the solid wastes or waste stream originated from those noted sources:
______________________________________ Category 1 ferrous material Category 2 light, porous, water-absorbent, non- putrescent organic material such as paper, cardboard, foam rubber and textiles Category 3 heavy, non-porous, non-water-absorbent, non-putrescent organic material such as rubber, plastic and wood Category 4 magnesium Category 5 aluminum Category 6 an assortment of heavy metals such as zinc, zamac, lead, copper, nickel, bronze and stainless steel Category 7 non-metallic inorganic material such as glass, sand, stones, bricks, concrete, porcelain and ceramics Category 8 putrescent organic material of a relatively high moisture content such as food waste, garden waste, agricultural waste and sewage ______________________________________
Of the various unit operations that may be assembled into a separation and recovery process for solid wastes and waste streams, none has any mandatory application or universal recognition when cost (both capital and operating), variation of feeds, and degree of separation possible without intermixing, among other factors, are considered.
Known separation devices such as eddy current concentrators, for example, have very poor ability to separate components and minimize separation product intermixing, when used in solid waste or waste stream environments. For example, eddy current concentrators often put 5% to 15% non-ferrous metals in an organics product stream, and as much as 20% to 30% organics in the non-ferrous metals. This poor separation then necessitates further, time-consuming and expensive processing to secure product streams of the necessary "cleanliness" and/or "purity," with minimal (if any) intermixing of other waste components.
Separation by density (or specific gravity/relative density), applied to solid wastes and waste streams, has some credence in the prior art These unit operations broadly involve the use of separation vessels with liquid media of a selected specific gravity.
European Patent Application EP 0 618 010 A1, published Oct. 5, 1994, describes a method and installation for separating materials, including solid wastes and waste streams, such as ferrous and non-ferrous scrap (col. 1, ll. 3-16). The application discloses a system that introduces a waste stream into a dose-measuring device 6, then in sequence to a magnetic separator 3, a mechanical sifting device 4, an aerodynamic separation device 5, and a single heavy liquid medium separation vessel 2 (Abstract; FIGS. 1-8), to recover a variety of streams from the waste (see FIG. 1, products 16, 24, 29, 46, 91 and 102; only products 91 and 102 result from the heavy liquid medium separation vessel 2 (FIG. 7)). While adjustment of the liquid medium's average density is disclosed (col. 7, ll. 41-57), and the separation of materials having an average density of between 1.0 and 1.7, up to 3.5, is addressed (see also col. 1, ll. 30-41), there is no disclosure of the use of multiple heavy liquid medium separation vessels, or subjecting the materials to be separated to more than one such separation stage. Use of the particular system disclosed is described as one of the key advantages offered by the invention: "The precise sequence of steps, with the intervention of other steps or not, allows an optimal separation of scrap with a minimal number of machines" (col. 1, ll. 28-30).
Plainly, there is no suggestion or teaching that additional capital expenditure be undertaken to carry out multiple heavy liquid medium separation stages, nor any suggestion that additional or other desired fractions/components could be recovered from the heterogenous solid waste or waste stream residue after the processing through the system and vessel 2 is completed.
Many conventional devices exist to effect density separations. These devices may be classified into two major groups: those employing a dynamic effect, and those employing only a small or essentially no dynamic effect. The former devices cannot be used to make a precise separation involving materials having very close specific gravities, for example materials differing in specific gravity by only one or two points to the third decimal place, since the dynamic effect can never be controlled uniformly over and against particles of varying sizes and shapes and/or densities. The latter classification, generally known as heavy liquid media separation processes, minimizes considerably the difficulties posed by particle size and shape.
A heavy liquid medium separation process, in its simplest form, involves a relatively quiescent liquid bath into which the materials to be separated are introduced. The liquid medium has an average specific gravity approximately intermediate that of the specific gravities of the fractions of feed whose separation and recovery is sought. The liquid medium usually has two principal components: the liquid, often water, and a suspension-creating, solid particulate material whose quantity and concentration is controlled to provide, taken with the liquid, the required specific gravity for the medium. Those materials with a density higher than the density of the bath liquid, sink, creating sink particles or "sinks", whereas materials with a density lower than the density of this separating suspending medium, float, creating float particles of "floats."
The most commonly used liquid media on a commercial scale are comprised of colloidal or semi-colloidal solids in suspension in water. Solutions are not viable commercially due to their high cost and their inability to be recycled or disposed of in an environmentally safe manner. Cost effectiveness and process viability of real-world systems require that the suspension-creating solid particulate media be inexpensive, readily available, and easily recoverable from the medium's liquid and/or from the separated and recovered fractions of the processed waste.
By properly selecting these colloidal solids, liquid media suspensions with a specific gravity of 3.2 can be generated which have sufficient liquidity/low viscosity to effect reasonably good separations, usually through the use of expensive media such as magnetite, ferrosilicon or mixtures of the two materials. Use of magnetite and ferrosilicon as the solid particulate suspension media to generate liquid medium suspensions for various suspension densities for coal beneficiation, metallic ore concentration and specialized ore beneficiation/diamond recovery, was known in the art Also known was the difficulty in controlling viscosity of the liquid media, dependent upon the type of suspension agent and upon the average specific gravity to be reached/attained: the presence of clay in such media was often suggested but could cause Theological problems requiring expensive reagent additions to control. See Burt, "Operational HMS Suspensions," Gravity Concentration Technology, Elsevier (1984), pp. 68-72 (discussion of density classes of suspension for types of separation, use of magnetite, ferrosilicon, mixes, with ferrosilicon use being necessary for denser liquid media).
Heavy liquid media separation vessels may be categorized generally into three classes according to the basic geometry of a cube, a cylinder, or a cone; that is, rectangular baths, horizontal rotating drums, and separator cones. Within these broad descriptions, a wide variety of separation vessels are known to the art, displaying different levels of operability and ability to separate and recover desired fractions from the feed with clean differentiation/purity of each fraction, with minimal or no intermixture. All three of those heavy-media device types are generally considered to be surface separation devices, for they involve a separation at or just below the surface of the separating medium.
All surface separation devices require a dynamic effect to carry the float particles across the surface of the vessel to some point of overflow or discharge. This dynamic effect can be generated by the forward or outward movement of the separating medium itself as it flows to some point of overflow or discharge. In every case, however, this dynamic effect disturbs the surface of the bath, and, since separation takes place in close proximity to the surface, the accuracy of separation to produce fractions with clean differentiation/purity is severely undermined. This problem is further compounded by the violent entry of the feed material into the separating zone of the vessel. In most cases the feed material is introduced at or just below the surface of the liquid medium, at only a single point of entry into the separating zone, thereby creating a relatively violent introduction of the feed material and undesirable turbulence.
Of the three general classes of heavy liquid media separation vessels, the separator cone, owing to its large surface area available for separation, is the most accurate in handling slow-settling, small sized, and near-gravity particles. A cone, however, imposes severe constructional limitations since it demands a significant height in order to enlarge the area of the separating zone and to provide sufficient angle needed for the gravity fall of the sinks. It is also undesirable as a separator because the vessel rise rates and vessel settling rates are at no point the same. Without substantially uniform vessel rise rates and settling rates, all possibility of an accurate separation is forfeited.
Overall the most common vessel shape within heavy media separation is that of a horizontal scrolled barrel. Known scrolled barrels were mono- or bidirectional. Mono-directional barrels were constructed in such a manner that both the floats and the sinks moved in the same direction and exit on the same end of the barrel. Bi-directional barrels had floats and sinks moving in opposite directions relative to one another, and consequently the floats and sinks each exited at opposite ends of the barrel (In a bi-directional barrel the floats at the surface of the bath stream across the length of the barrel mid-section until they reach their point of overflow at the floats discharge end of the vessel, whereas the sinks at the bottom of the bath are screwed in the opposite direction by means of scrolls until they reach the sinks discharge end of the vessel.)
Burt, "Heavy Medium Separation," Gravity Concentration Technology Elsevier, 1984, pp. 139 et seq., discusses the basic parameters and characteristics of that operation. In an introduction, he states that:
The upper size limit is related to the liberation of the constituents in the ore to be separated, although separations coarser than 300 mm are not common. The lower size limit of the process is generally accepted to be 0.5 mm (for dynamic heavy medium); however, even this bottom size is more a function of effective classification and medium recovery than of the process itself.
Page 139
No indication of the potential usefulness of this operation in a system or process for separating and recovering/recycling solid wastes or waste stream fractions/components appears, the prior art recognition of utility being limited to coal and industrial mineral applications, for end product or waste product production.
Commenting that "In principle, heavy medium separation is the simplest of all gravity concentration processes," Burt described the differences between static heavy medium separation, and dynamic heavy medium separation, which was defined as "heavy medium separation carried out at elevated gravitational force normally in a cyclonic separator" (p. 140):
Page 141
Burt considered heavy medium separation not to properly be identified as a unit operation, but rather to constitute a complex "system" with a series of interconnected phases: (a) feed preparation; (b) feed and medium presentation; (c) separation of heavies and lights in a suitable vessel; (d) product recovery; and (e) medium recovery. Describing general operation of a heavy medium separation circuit, Burt reported that:
Page 142
Plainly, Burt reflects a narrow prior art view of the process and system details that must be used with heavy medium separation, comprehending little or no flexibility.
Burt also extensively discussed the then-known separation vessels for heavy medium separation, breaking them into two main classes of static and dynamic vessels:
Page 149
The teaching of use of cone separators where large quantities of floats are expected, and drum separators where large quantities of sinks are expected, teaches away--actually, lacks any teaching--of vessel choice where one or more vessels in series may be needed and the quantity of floats to sinks varies from approximately the same to one and then the other present in a major quantity.
An extensive review of cone (pages 100-152) and trough separators (pages 156 et seq.) brackets Burt's description of drum separators, which focuses upon the Wemco drum as typical of drum separators. Noting, first, that:
Page 153
The Wemco drum in its one or two compartment configuration is discussed, together with its possible use for two or three product separations:
(a) on dual-gravity operation: new feed material is fed to the first compartment for low gravity separation. The sink product from this compartment is elevated by the lifters and feeds into the second compartment for high gravity separation. (FIG. 9.6b). PA2 (b) on single-gravity operation, either the same feed or a different sized feed is fed into each compartment operating at the same density (Wilson 1978b).
Page 153
No particulars are given as to feed introduction or floats/sinks removal, nor is there any recognition or teaching that such may effect through-put and/or perfection/cleanliness of possible separation.
Among the other drum separators described was a "counter current separator":
Page 155
No controlling preference for any specific vessel was expressed by Burt, but a statement of basic requirements was made:
Pages 149-150
Prior art rotating drum separation vessels of various configuration used to effect separation of various materials were known. Pelletier, U.S. Pat. No. 4,323,449, Method and Apparatus for Beneficiating Coal, issued Apr. 6, 1982, disclosed the use of a rotating, sloping barrel separation vessel (FIG. 1) having internal spiral/helical flights and frustoconical, foraminous (screen-like) end sections, which function as built-in trommelscreens, into which vessel a mixture of the coal and ash to be separated, and a denser material/liquid medium, were deposited. The coal, which floats, travelled downwardly in the vessel, while the ash material, which sinks, was screwed spirally upwardly. Separation was carried out using the heavy liquid medium concept (col. 1, l. 53--col. 2, l. 4). The system and continuous process disclosed (FIGS. 4A, 4B), used only one separation vessel; the liquid medium had a specific gravity of about 1.2 to about 1.65 (col. 6, ll. 1-5), the specific gravity used being selected "depend[ing] upon the specific content of the ore material being separated." Control of speed of rotation, angle of the slope of axis of the barrel, and the location of deposit of the ore material and the medium into the vessel in combination with the density of the medium, enabled separation of varying coal mixtures, especially where substantial amounts of coal fines were present (col. 3, ll. 8-14).
Pelletier's system was capable of processing only a feed mixture that had one desired product to be recovered - coal, in various sized particles, including fines, from gob piles, and other coal pits and discard locations (see col. 2, ll. 846), with no further separation and recovery of other materials described, or contemplated, from a heterogeneous feed such as presented by solid wastes and waste streams (see col. 1, ll. 9-29; col. 2, ll. 30-46).
Pelletier focuses on an "on the fly" variation in the specific gravity of the liquid medium in the single vessel, to avoid problems presented by variations in gob pile materials and quantities of particular materials (col. 2, ll. 15-19), so as to only need one vessel in his system to extract the desired coal: "The density of the medium added to the barrel 12 is adjusted in accordance with the content of the ore material being treated. The medium is adjusted while it is stored in the tank 150 through selective adjustment of the valve 182 controlling make-up water flow to the medium tank 150" (col. 8, ll. 47-53; cf. col. 2, ll. 24-29). This continuous variation and adjustment of the specific gravity of the liquid medium in one vessel would adversely affect both vessel through-put and a vessel's capability to consistently produce clean/perfect separations of fractions/components on the basis of specific gravity difference, where a heterogeneous feed with multiple desired fraction/component streams was processed.
In fact, where a particular feed combination of coal and ash constitutes a "difficult to separate mixture" (col. 6, l. 20 et seq.), Pelletier teaches adjustment of the barrel angle to increase residence (dwell) time, which concomitantly cuts back on vessel through-put, an adverse result in a continuous process (see col. 6, ll. 14-27). The necessary variation of angle and rotation speed, when confronted with a change in feed characteristics, also requires more complicated control approaches and apparatus.
La Point, U.S. Pat. No. 4,018,567, Apparatus for Separating the Constituents of Lead-Acid Storage Batteries, issued Apr. 19, 1977, disclosed a system and process for treatment of whole or shredded lead-acid batteries, which does not require draining of the acid as an initial step before treatment. It combined physical separation of lead-acid battery components with simultaneous chemical treatment of lead sulfate and neutralization of the electrolyte in the batteries, to facilitate recovery of the lead values therein (col. 1, ll. 20-25).
The reaction and separation device comprised a rotatable drum having first and second ends (FIGS. 1-2), the first end having a combined feed and discharge opening, the second end having a separate discharge opening. First and second trommelscreens were affixed externally to the ends of the drum, fitting over the openings. A charge of grinding balls was placed in the drum before operation, which balls were necessary to further fracture and break down battery components and batteries fed to the device (col. 3, l. 59--col. 4, l. 12).
Means were provided to feed whole or shredded batteries to the drum, through the opening in the first end, together with sodium carbonate and water. The process separated constituents fed in, into three distinct and substantially uncontaminated streams of antimonial lead, active material and organic material (col. 3, ll. 3-8), combining a hydromechanical separation of the battery constituents with chemical treatment to eliminate lead sulfate and battery acid in the same processing vessel (col. 3, ll. 9-13, 25-37; col. 6, ll. 26-40). (The active material consisted of lead, lead oxide and lead sulfate; the organic material consisted of the battery case and separators (col. 3, ll. 18-25)). The suspension density of the bath was preferably maintained at from 1.4 to 2.0 (col. 7, ll. 55-57). A helical scroll on the internal drum surface, aided by longitudinal lifter bars, advanced sinkable battery fragments toward the second end of the drum until obstructed by a transverse baffle plate which restricted further passage to all material larger than a predetermined size, which had the effect of concentrating larger fragments for efficient break-up by the grinding balls. Means were also provided to lift up smaller fragments and deflect them through the second end and out of the vessel (col. 4, ll. 3-13).
La Point emphasized that use of multiple units of equipment to process waste batteries necessarily degraded the efficiency of the method, while presenting undesired space requirements (col. 1, l. 67--col. 2, l. 10). Further, he stated that "obviously, it is desirable in this highly competitive field to devise a method and apparatus for recovering lead values from storage batteries which reduce the initial capital outlay and operating costs to a minimum, Clearly, therefore, an important characteristic of such method and apparatus ought to be the maximum simplicity in processing consistent with the production of lead values of high purity." (col. 2, ll. 3-10). As a consequence, La Point taught away from any use of more than one separation vessel performing a single hydromechanical separation (simultaneously with the chemical transposition of lead sulfate particles into lead carbonate (col. 3, ll. 26-37)). The stated general object of the invention confirm this "one vessel only," one stage only teaching:
(col. 2, l. 67-col. 3, l. 2)
Both Pelletier and La Point, then, affirmatively directed one of ordinary skill in the art away from any system or process using more than one separation vessel and/or more than one separation stage to, inter alia, effect a heavy liquid medium separation.
Much work has recently been done by the inventor in researching the specific, key characteristics of separation vessels comprising a bidirectional heavy liquid medium separator (which work does not constitute prior art to this invention). Cf. Olivier, U.S. Pat. No. 5,373,946, System for Media Separation of Solid Particles, issued Dec. 20, 1994 (the "'946 patent"); Olivier, U.S. Pat. No. 5,495,949, System for Treating Solid Particles in a Medium, issued Mar. 5, 1996 (the "'949 patent"), each of which is incorporated herein by reference. The bi-directional heavy liquid medium separation vessels disclosed in the '946 and '949 patents, when constructed have a number of features and characteristics that favor a near perfect heavy liquid medium separation having a clean differentiation/purity of fractions by satisfying a number of requirements:
Bi-directionally offers other advantages. De-watering and/or rinsing devices can be situated on both sides of the barrel easily handling a situation of almost 100% floats or 100% sinks. This translates into very large input tonnages; 6 ft-, 8 ft- and 10-ft diameter barrels can handle 75, 150, and 300 TPH of input respectively.
The bi-directional heavy liquid medium separation vessel however, while it may hold out the potential of substantially perfect separations of feed particulates at a given specific gravity of the liquid media, is not itself a solution to the problem of separation and recovery/recycling of a series of components of automobile, industrial commercial construction, demolition, agricultural and municipal solid wastes and waste streams. Separation and recovery/recycling of only a part of a solid wastes and waste stream leaves a residue of material that still must be disposed of. Disposition of the entire waste solids and waste stream in one system and process is the problem that the art has as yet failed to resolve.
An overall system and process, to solve that problem, must be capable of a series of separations, including sequential separations on a first separated stream or fraction, to recover a variety of fractions and product materials from the heterogeneous feed mixture of particulate solids. The separations and recovery of the fractions must be such as to be as close to perfect/clean as is practicable, with minimal or no intermixture of product streams. The overall system and process must have the flexibility to handle varied quantity of components and nature of components in the feed solid wastes and waste streams, without substantial diminution in separation efficiency or perfection/cleanliness of separation. An overall system and process must have maximum cost effectiveness, including effective recovery and recycle of the heavy liquid medium densifying or suspension creating material, which is a particulate solid. In high through-put solid wastes and waste streams systems and processes, the cost economics of the treatment system often defeat the system and process efficacy, because the volumes at issue magnify small cost negatives, viewed on a unit basis, into a substantial impediment to the system. For example, the need for expensive components needed to carry out a separation, if those components cannot be separated, recovered and recycled, teaches away from use of any particular unit operation in a waste treatment system. If a sequence of such operations would be necessary to accomplish necessary separations and recoveries, one of skill in the art is strongly motivated to avoidance of that operation and that sequence in repeated separation stages, as the negative economics increase in direct proportion to each repeated use.
The sequence of separations, the apparatus used to carry out each separation, the apparatus used to remove, recover and recycle the suspension creating material, and the specific gravity of liquid medium selected in each separation, all present substantial variation and difficulty even if one somehow was led to pick-out a density separation technique from the myriad known in the art to provide general basis for an overall system and process that disposes of an entire solid waste and waste stream.
In fact, conventional wisdom and knowledge in the art teaches away from the use of a heavy liquid medium separation-based system and process in a number of situations, particularly where solid wastes and waste streams include light, porous materials, such as foam rubber and textiles. The prior art understands that light porous materials should not be allowed to enter a heavy liquid medium separation vessel for three (3) reasons:
Instead, air separation is the prior art recognized and accepted unit operation for separating light porous materials from solid wastes and waste streams, the method being recognized to have a number of advantages favoring isolation of light porous materials.
There remains, then, the need for a system and process capable of separating for complete recovery/recycling a heterogeneous mixture of particulate solids from solid wastes and waste streams, those solids having a plurality of different specific gravities, effectuating in that system and process a plurality of clean/pure separations on the broad range of materials found in such solid wastes and waste streams, which differ only slightly in specific gravity and which must be separated in a high through-put, cost-effective way on an industrial and commercial scale.